Highway crossing protection apparatus

ABSTRACT

Each approach detection track circuit in a multiple track stretch crossed by one or more highways is sequentially connected to a track energy source, including a distance monitor means, by a multiplexing means, shown as a bank of relays operated in repeated cycles by a central process controller. The distance monitor, as it is sequentially connected to each track circuit, provides a distance proportional signal to the central process controller for a train approaching along any track. The process controller registers the detection of the approaching train and determines its continued approach by successive distance measurements received from the same track circuit. When the train is determined to be a predetermined warning time or distance from the crossing, the process controller actuates the highway warning signals. Multiplexing the connections of the track circuits to the distance monitor allows the use of a single set of centralized highway crossing apparatus including the distance monitor and the process controller.

United States Patent Staples et al.

HIGHWAY CROSSING PROTECTION APPARATUS [75] Inventors: Crawford E.Staples, Edgewood;

Donald E. Stark, Penn Hills Township, Allegheny County, all of Pa.

[73] Assignee: Westinghouse Air'Bralre Company,

Swissvale, Pa.

[22] Filed: May 8, 1972 [21] Appl. No.: 251,369

[52] US. Cl 246/130, 246/125, 317/140 [51] Int. Cl B611 1/06 [58] Fieldof Search 246/125, 128, 130,

[56] References Cited UNITED STATES PATENTS 2,887,571 5/1959 Bettison etal. 246/130 R 3,603,786 9/1971 Peel 246/128 3,619,604 11/1971 Auer etal.246/122 R 2,424,243 7/1947 Lowell 317/137 3,342,989 9/1967 Dwyer et al246/122 R Primary Examiner-Robert G Sheridan Assistant Examiner-GeorgeH. Libman Attorney-1'1. A. Williamson et al.

[111 3,781,543 1 Dec. 25, 1 973 .detection of the approaching train anddetermines its continued approach by successive distance measurementsreceived from the same track circuit. When the train is determined to bea predetermined warning time or distance from the crossing, the processcontroller actuates the highway warning signals. Multiplexing theconnections of the track circuits to the distance monitor allows the useof a single set of centralized highway crossing apparatus including thedistance monitor and the process controller.

9 Claims, 2 Drawing Figures 1 HIGHWAY CROSSING PROTECTION APPARATUSBACKGROUND This invention pertains to highway crossing protectionapparatus. More particularly, our invention relates to protection and/orwarning arrangements for com plex rail and highway crossing layouts, forexample, multiple tracks with different speeds of approach or pluralhighway crossings within overlapped warning distances, using a minimumamount of apparatus by multiplexing the detection and control processesto the various approach track stretches.

There is an increasing demand for protecting highway users at gradecrossings with railway tracks. This is partly because of public opinionregarding the reduction of highway accidents. However, there does exista positive need for increased safety, both for highway users and trainoperation, which requires active crossing warning systems rather than amere passive or inert wayside sign along the highway. Ideally, ofcourse, a complete grade separation of the highway and railroad tracksis the ultimate safety solution but the physical conditions at manycrossings do not permit such improvements. The resulting need,therefore, is to improve the operation and reduce the costof highwaycrossing protection apparatus arrangements. The reduction of cost isparticularly necessary at complex crossing situations where there may bemultiple railroad tracks, that is, two or more parallel tracks; wherethere is a plurality of highways crossing with overlapped warning areasalong the single stretch of track; and finally within urban areas wherethe two situations are frequently combined. A related requirement, ofcourse, is for uniform warning times at any crossing, without regard tovarying train speeds and multiple crossings, so that the effectivenessof the warning indication upon the public remains constant and undueperiods of waiting will not cause drivers to ignore such signals. Onesolution for reducing the cost of complex installations is the use of acentralized set of detection and control apparatus that may be timeshared over several approach stretches or at the various highways in aplural and complex physical layout. Such centralized apparatus, ofcourse, provides an economicadvantage in reducing the total apparatusrequirement and has an operational advantage in that a centralizedsignal control process may be used having preset warning I conditions.

Accordingly, an object of our invention is an improved highway crossingprotection arrangement.

Another object of the invention is a crossing protection arrangementproviding improved operation at complex grade crossing layouts.

Still another object of our invention is highway crossing protectionapparatus using centralized train detection and warning signal controldevices time shared between several approach tracks and/orgradecrossings in a single area.

. It is also an object of our invention to provide highway crossingprotectionusing centralized detection and signal control apparatus toprovide substantially uniformwarning at each of several adjacenthighways intersectinga'single stretch of railroad track.

, Yet another object of the invention is an arrangement at highwaycrossings for detectingapproaching trains on any one of a plurality oftracks intersecting the highway, using a single set of distancedetection apparatus coupled in sequence to each of the several approachtrack sections.

A further object of our invention is a highway crossing warningarrangement including single train distance detection means connected insequence by multiplexing means to each of a plurality of approachsections in several parallel tracks intersecting the highway.

It is a still further object of our invention to provide, usingcentralized train detection and signal control means time shared overvarious approach track stretches, a relatively uniform warning signaloperation at each of several highways intersecting a plurality ofparallel tracks over which trains move in each direction across all ofthe highways.

Other objects, features, and advantages of our invention will becomeapparent from the following specification when taken in connection withthe accompanying drawings and appended claims.

SUMMARY In practicing our invention, a central process controller meansincluding suitable input and output interface apparatus is provided forcontrolling the warning system for the highway crossing complex. Asingle distance monitoring device is used to detect the approach oftrains toward the crossing or crossings and to provide an output signalproportional to the distance of the train from the crossing. A minimumwarning time and- /or distance for each possible approach ispredetermined andset into the system, that is, into the processcontroller. In the principal showing, the distance monitoring device isconnected in a repeated sequence to detector track circuits installed ineach approach to the crossing along a plurality of parallel railroadtracks. One track circuit at a time is connected to the distance monitorby a multiplexing means, shown as a bank of relays controlled by theprocess controller. Each track circuit is operable for detecting a trainwhen energized through the distance monitor, and also to provide thedistance monitor with a signal for determining the distance to theapproaching train. The train distance signal is fed in digital form intothe process controller which compares successive distance measurementsto determine the speed of the approaching train and thus the time priorto its arrival at the crossing. When the determined arrival time of atrain is equal to the predetermined minimum warning time for thecorresponding approach, the process controller actuates the warningsignal means to indicate to highway users that a train is approachingwithin the preset distance or time. If a plurality of closely adjacentcrossings are positioned along the stretch of track soas to haveoverlapped approach sections or distances, a minimum time for eachcrossing is set into the controller so that, with the single approachdetection track circuit, the various warning signals at each crossingmay be individually actuated at the proper time during the passage ofthe train. The signal control process may also include a detection oftrains entering the stretch from a spur track within the approaches todetermine which and when various crossing signals are actuated.

DETAILED DESCRIPTION- We shall now describe the arrangement of ourinvention in more specific detail, prior to pointing out the novelfeatures thereof in the appended claims, referring from time to time tothe accompanying drawings in which:

FIG. 1 is a diagrammatic circuit representation of a crossing warningsystem for a multiple track crossing by a single highway embodying thearrangement of our invention. 4

FIG. 2 is a schematic illustration of a multi-crossing installationalong a stretch of track, to which the invention is applied using adifferent type of detector track circuit.

I In each of the figures, similar items are designated by similarreference characters.

Referring to FIG. 1, three parallel railroad tracks, each shown by adouble line representation, are illustrated as intersected by a highwayH, which is also shown by a double line symbol. A warning signal deviceis located along the highway on each side of the railroad tracks to'warn highway traffic moving in each direction of the approach of atrain. These signal devices, designated as G1 and G2, are shown byconventional symbols as well-known flashing light apparatus. It isunderstood, of course, that other types of warning signals areavailable, forexample, automatic gates in addition to the flashinglights may be provided, and the-use of any such alternate or additionalwarning apparatus is included in the arrangement of our invention; Thenecessary and proper operating controls for the warning signals aresupplied through an-input-output interface apparatus from a centralprocess controller, which will be discussed later.

Since trains may move in either direction on each of the three tracks,the detection of trains approaching from either side of the highway mustbe accomplished. For this purpose, a detector track section in eachdirection along each track is provided, separated by the insulatedjoints J shown in each rail immediately to the right of highway H. Eachapproach track section is terminated by a shunt S connected between therails at the distant end of the section, the points of connection of theshunts being predetermined in accordance with allowable train speeds andthe desired detection times. Each track section is designated by thereference T with a prefix in accordance with the track number, in

sequence, from the top, and an indication as to whether the sectionextends to the west (left) or to the east (right) of the highway. Forexample, in the upper or track No. l, the two approach'detector sectionsare lWT, extending to the left, and lET, extending to the right.

Each track section is provided with a track circuit for the detection ofapproaching trains. Since energy, as will be described, is supplied fromthe highway end and with a permanent shunt across the distantend, eachtrack circuit is of the type which permits the measurement of thedistance to the permanent shunt or to an intervening shunt provided bytrain wheels and axles. Each track circuitis normally deenergized andenergy is supplied periodically through a distance monitor device, shownas a conventional block so labeled. This energy is preferably analternating current of a preselected frequency which will permit anindication of the distance to the rail shunt. The distance monitordevice is shown by a conventional block since the detailed circuitrythereof is not a particular part of our invention and may be of anyknown type. For example, one such device is shown in Letters Patent ofthe U.S. Pat. No. 3,342,989, issued Sept. 19, 1967, to E. C. Dwyer andB. Mishelevich, for a Track Fullness System. Another type of suchdistance monitor devices which may be adapted to use in the presentlydisclosed arrangement is shown in Letters Patent of the U.S. Pat. No.3,155,350, issued Nov. 3, 1964, to R. D. Campbell, also for a TrackFullness System. Either of these disclosed distance measuring means orany equivalent apparatus may be adapted for use in an arrangementembodying our invention.

Although direct rail connections may be used, energy is normally coupledto therails of each section through a track transformer. Herein each isdesignated by the reference T with a combined suffix including the tracknumber and a letter W orE, designating the associated west or east tracksection, respectively. For example, for track sections IWT and lET, thetrack transformers are designated by the references T1W and Tl E,respectively. The secondary of each transformer is connected across therails, the two secondaries in each track being insulated from each otherby the joints J. The primary of each transformer is periodicallyconnected to the source of alternating current energy through thedistance monitor device.

Thetrack circuits may be considered to be normally deenergized sincethey are only periodically supplied with energy from the distancemonitor apparatus which serves as a constant current source. Thesequence of application of energy to the various track circuits, thatis, their connection to the distance monitor apparatus, is controlled bya multiplexer means, shown specifically as a bank of relays A, B, and C.These relays,'in their sequencing operation, are illustrated as beingcontrolled through the interface circuitry by the process controller,which is to be discussed later. The time sharing or multiplexingconnection sequence for supplying energy from the distance monitor tothe track circuits is actually performed by the matrix of contacts ofrelays A, B, and C. The contact matrix connections, as shown, are forbinary operation of the relays with relay A representing the leastsignificant binary digit, and relays B and C being of increasingsignificance in that order. Since only six track sections or trackcircuits are specifically illustrated, two of the possible eight codecombinations of the three relays in binary operation are unused.

Thefirst multiplex circuit connection used is that with relay A aloneenergized, designating the binary code 1. Under these conditions, energyis supplied to the track circuit of section 2ET from terminal BX of asuitable alternating current source, which may be a commercial frequencysource, through the distance monitor and over front contact a of relayA, back contact a of relay B, back contact b of relay C, and the primaryof transformer T2E to terminal NX of the alternating current source.During the immediately following relay code combination, relay B aloneis picked up, signifying a binary 2. The completed circuit now includesback contact a of relay A, front contact b of relay 8, back contact 0 ofrelay C, and the primary of transformer TIE, so that the track circuitof section lET is supplied with energy. During the next relaycombination representing binary 3, relays A and B are both picked up andthe circuit over front contacts a of these two relays and back contact aof relay C supplies energy to the primary of transformer T3E for thetrack circuit of section 3ET. The binary 4 combination, relay C alonepicked up, is not used in this specific showing. During the followingrelay combinations, the track circuits for sections ZWT, lWT, and 3WT,in that sequence, are energized, as may be traced by reference to thedrawing. The binary 0 combination of all relays released is also notused. However, the possible circuit connections shown from back contactb of relay B by dotted lines, including front and back contacts d ofrelay C, could provide energy to two additional track circuits duringthe herein non-used relay combinations. The cycle of relay operation inthe multiplexing arrangement normally immediately repeats and suchcontinuous repeating of the cycle occurs under control of the processcontroller to periodically provide energy to detect train approachthrough each of the track sections. Obviously, other relay operationalsequences can be used and the contact matrix connections revised toaccommodate such operations. As each track circuit is energized duringthe sequential operations, the distance monitor device checks for trainapproach detection and develops a distance measurement signal to thepermanent shunt S or to the shunt resulting from the entrance of a traininto the section.

Although shown as a bank of relays, obviously other switching apparatusmay also be used as the multiplexing means. For example, transistors orcontrolled rectifiers can replace the relay contacts and the gating ofsuch devices in selected sequence controlled by signals from the processcontroller. Further, the multiplexing means, relay or solid state, canbe designed, if desired, to be free running or self operating through atleast the normal predetermined sequence without control signals from theprocess controller. This latter device could then exercise specificcontrol to vary the normal sequence if extra scanningof specific trackcircuits is desirable, e. g., one occupied by a train. If free running,the multiplexer would of necessity indicate to the process controllerthe step or condition in the normal sequence to which it had advanced.

The process controller means, shown in the lower left of FIG. 1, is, theheart of the control for the crossing system, determining whenthewarning signals are actuated to provide sufficient but not excessivewarning time to highway users. The degree of sophistication of uniformoperating time desired in any particular installation fixes therequirements for the process controller operation. This device is hereinshown by a conventional block since it may be any one of different typescomprising known circuit elements. The operation desired can be providedby any of the types known and it is the operation only, and not thespecific circuit details which are included as part of our invention.This process controller may be either a hard wiredor a stored programapparatus. In either case, the operating functions provided are thesame. This device sorts the incoming data, particularly the traindetection and distance information, and registers it on a per trackcircuit basis. It calculates the distance to the approaching train andprovides for scaling of the individual approaches where theircharacteristics differ. By comparison of the successive distancecalculations for a track, the veloc ity of an approaching train and itsdirection of travel may be determined. Once the distance, velocity,and/or way traffic. The process controller, of course, provides theactuating controls for the warning signal devices, the control being ofa nature to match the type of signal provided. The process controlleralso controls the sequential track circuit scanning cycle by controllingthe operation of the multiplexer, here relays A, B, and C. Ininstallations where several highway crossings exist in relatively closerelationship along the same stretch of tracks, the functions of thecontroller can provide implementation of the different highway warnings,without having separate track circuits, by being programmed with therequired sequencing and timing for actuating and clearing the successivesignals during the passage of a particular train.

The distance proportional signal or indication provided by the distancemonitor for any particular track circuit is digitized by the analog todigital converter and then applied through the interface to the processcontroller. The digital output may be of binary form but is not limitedto this type of digitizing. The resolution of the converter is such asto provide measurements of the precision necessary to establish thelocation of the approaching rail traffic to the accuracy required by theoverall system requirements. The analog to digital converter is shown bya conventional block since the specities of the circuitry depend uponthe type of distance monitor used and the required accuracy of theconversion for input to the process controller. Since such convertersare well known in the art, the selection of the specific type requiredmay be made during the design engineering for a particular highwaycrossing installation.

The input and output interface apparatus, also shown by a conventionalblock, provides the interconnection between the distance monitor andassociated analog to digital converter outputs and the processcontroller and also couples the outputs from the process controller tocontrol the multiplexing relays and the various highway signals. Thespecifics will depend upon the requirements of the individualinstallation, the type of process controller used, and thecharacteristics of the input and the output signals developed. The inputportion of the interface accepts the digital data from the A/D converterand passes it to the process controller. The output portion of theinterface provides for control of the multiplexer relays and for thecontrol of the other external equipment, such as the warning signalswhich may include crossing gates, flashing lights, and bells. The energylevels and power handling capabilities of the various circuits areproportioned to accommodate the need of the devices they control. Inaddition, the interface may also contain supplementary apparatus, suchas times and flashers, for control of the warning signals. As indicated,the size and sophistication of the interface circuitry and apparatuswill depend upon the type of process controller selected and the signalsrequired for operation of the various external apparatus. FIG. 2 shows asingle track stretch intersected by a plurality of highways H1, H2, andH3, which are in relatively close proximity to each other. Although onlya single track is shown, obviously the several highways could intersectparallel tracks, such as are shown in FIG. I. It has already beenmentioned that the process controller embodied in the arrangement of ourinvention can be wired or programmed, depending upon its type, to handlea situation such as shown in FIG. 2. Under these conditions, the properactuation of the warning signal at each highway, in order to providesufficient warning of proper duration to the highway users as the trainpasses along the stretch, can be accomplished.

Also shown in FIG. 2 is an alternate type of track circuit which may beused when it is desired to avoid any interference between traindetection for the highway crossing warnings and the regular trackcircuit detection of the railroad signal system controlling the movementof trains. Although shown inthe specific circumstances illustrated inFIG. 2, such a track circuit may actually be substituted for the pair oftrack circuits in each one of the parallel tracks shown in FIG. 1.Specifically, each track circuit shown in FIG. 2 is of a center fed typeand the connections from the secondary winding of the track transformerT1" span the width of the associated highway to provide positivedetection over the crossing without requiring multiple track feeds orother special handling. A tuned shunt TS is shown at each distant end ofthe approach track sections since it is intended that the energy sourcewill supply audio or higher frequency current for overlay track circuitoperation, which is well known in the art. Such overlay track circuitsinclude no insulated joints and thus do not interfere with the regulartrain detection track circuits of the railroad signal system. Thecapacitor shown in series with the secondary of each track transformerTT, in conjunction with the inductance of the transformer winding,provides a high impedance to signals of other frequencies which may beused for train detection in the train signal system, and thus preservesthe integrity of the train detection track circuits otherwise in use.Dependingupon the existing circumstances, the energy source for eachtrack circuit may be coupled or connected to the rails by other knownarrangements.

Three distinct track circuits are shown, one for each highway crossing.Each track circuit uses the same pair 4 of distant shunts TS but appliestrack current at the associated crossing. The secondary of eachtransformer TI is connected to the rails to span the associated highwayfor the purpose previously mentioned. Specifically, the secondaryconnections of transformer -'I'Il span highway 1-11; of transformer TT2,highway H2; and of transformer 'I'I3, highway H3. The primary windingsof transformers 'I'Il, TT2, and TT3 are supplied with energy in sequencefrom the distance monitor, with the sequence controlled by amultiplexingmeans such as the relays A, B, and C of FIG. 1. Thus eachtrack circuit is energized at a different time and no interferenceresults. Obviously, each overlay track circuit shown in FIG. 2 willdetect the presence of the train within the limits defined by thedistant tuned shunts TS and, in conjunction with the distance monitormeans which supplies track energy in sequence, provides a distanceproportional signal to the process controller for the installation. Thislatter apparatus, as previously described, then functions to calculatethe distance to the approaching train from any one of the highwaycrossings shown and actuates the corresponding warning signals at theproper time during the movement of the train through the stretch oftrack shown.

It will be understood by those skilled in the artthat a failure ineither type of track circuit, under which the track circuit becomes opendue to a break in a rail or interruption of the connection of the shuntacross the rails, will result in a much higher distance measurement fromthe distance monitor means. The process control ler may be programmed orwired to respond to such a fault condition to actuate the signals sincethe much higher distance indication will indicate a fault which maypreclude the detection of an approaching train.

The system of our invention thus provides an economical arrangement forproviding highway crossing warning signals for any highway crossinginstallation and particularly one which is of a complex nature due tothe presence of a plurality of parallel tracks and/or several closelyspaced highway crossings. The central process control means and themultiplex use of the train detection and distance monitoring apparatusreduces the total apparatus requirement for the whole installation. Atthe same time, the efficiency of the centralized process controller todetermine the distance and arrival time of approaching trains, and tocompare these with the. preset warning distances and times, allows theproper operation of the warning signals at each of several crossings andfor trains approaching over any one of the tracks. The finalresult thenis an efficient, effective, and economical highway crossing protectionapparatus.

Although we have herein shown and described but two forms of highwaycrossing protection apparatus embodying our inventive concept, variouschanges and modifications therein within the scope of the appendedclaims may be made without departing from the spirit and scope of ourinvention.

Having thus described our invention, what we claim 1. A highway crossingprotection arrangement for a highway intersecting multiple parallelrailroad tracks, comprising in combination,

a. a normally deenergized separate track circuit for each direction ofapproach to said highway along each parallel track, capable whenenergized of detecting the presence of a train within approach warninglimits,

b. a warning signal means along said highway operable when actuated fordisplaying a signal warning highway users of the approach of a train,

c. distance monitor means for at times individually supplying energy toa particular track circuit and responsive to the detection of a traintherein for determining the distance of the approaching train from saidhighway,

d. a mutliplexing means operable for sequentially coupling said distancemonitor means individually to eachseparate track circuit, and

e. a process controller means coupled for receiving .the approachingtrain distance information from said distance monitor means andresponsive thereto for actuating said warning signal means to displaythe warning signal when the train is a prose lected minimum time periodfrom said crossing.

2. A protection arrangement as defined in claim 1 in which,

a. energy supplied by said distance monitor means is an alternatingcurrent of preselected frequency, and

b. each track circuit includes,

1 a transformer for coupling said distance monitor means to the rails ofthe corresponding approach track section, and

2. a shunt connected across the rails at the end of the correspondingsection distant from the cross- 3. A protection arrangement as definedin claim 2 in which,

a. the separate track circuits for each direction of approach along eachparallel track are paired as a center fed track circuit, coupled to therails by a single transformer to form also a positive detector sectionincluding the actual crossing,

b. each shunt at the distant end .of each approach section is tuned tosaid preselected frequency, and

c. the rail connections of each coupling transformer include a seriescapacitor selected to inhibit the shunting of any other superposed trackcircuit of different frequency.

4. A protection arrangement as defined in claim 2 in which saidmultiplexing means includes,

a. a bank of multiplexer relays controlled by said process controllermeans for operating through a predetermined sequence of conditions inrepeated cycles, and

b. a contact matrix controlled by said relay bank for completing adifferent circuit path through said matrix for each sequential conditionof said relays,

0. each said circuit path connected for supplying energy from saiddistance monitor means to a different track circuit to detect anapproaching train in the corresponding section.

5. A protection arrangement as defined in claim 4 which furtherincludes,

a. interface apparatus coupling said process controller means to saidrelay bank and to said warning signal means, and

b. analog to digital converter means connected for receiving traindistance signals from said distance monitor means and operable inresponse thereto for converting each signal from analog to digital form,

1. said converter means being coupled through said interface apparatusfor supplying each digital distance signal to said processcontroller'means.

6. A highway crossing protection arrangement for a plurality of highwaysintersecting in relatively close proximity a railroad track, comprisingin combination,

a. a warning signal means along each highway opera ble when actuated fordisplaying a signal warning highway users of the approach of a train,

b. a normally deener gized detector track circuit for each crossingcapable when energized of detecting a train approaching that crossing ineither direction within limits of that track circuit,

c. a shunt connected across the rails at a location along said track aselected distance in each direction away from all said plurality ofcrossings for defining the distant limits of each track circuit,

d. distance monitor means for at times supplying en-' ergy to each trackcircuit and responsive to the detection of a train therein fordetermining the distance of that train from the associated highwaycrossing,

e. a process controller means coupled for receiving train distanceinformation from said distance monitor means and responsive thereto foractuating a selected warning signal means to display the warning signalwhen an approaching train is a predetermined time interval from thecorresponding crossing, and

f. a multiplexing means operable for sequentially coupling said distancemonitor means to each detector track circuit.

7. A protection arrangement as defined in claim 6 in which,

a. energy supplied by said distance monitor means is an alternatingcurrent of preselected frequency,

b. each shunt at the distant ends of said track circuits is tuned tosaid preselected frequency, and

c. each track circuit further includes,

1. a transformer for coupling said distance monitor means to the railsin a manner to form also a positive detector section spanning thecorresponding highway crossing, and

2. a capacitor connected in series in the rail connections of saidcoupling transformer to inhibit the shunting of any other superposedtrack circuit of different frequency.

8. A protection arrangement as defined in claim 7 in which saidmultiplexing means comprises,

a. a bank of multiplexer relays controlled by said pro- .cess controllermeans for operating through a predetermined sequence of conditions inrepeated cycles, and

b. a contact matrix controlled by said relay bank for completing adifferent circuit path through said matrix for each sequential conditionof said relays,

c. each said circuit path connected for supplying energy from saiddistance monitor means to a different track circuit to detect a train.

9. A protection arrangement as defined in claim 8 in which,

a. said process controller means is a digital data process controller,and which further includes,

b. interface apparatus coupling the process controller output to saidmultiplex relay bank and to said warning device, and

c. analog to digital converter means coupling said distance monitormeans through said interface apparatus to said process controller andoperable for changing the distance signal output of said distancemonitor means from analog to digital form.

=k l t l= i=

1. A highway crossing protection arrangement for a highway intersecting multiple parallel railroad tracks, comprising in combination, a. a normally deenergized separate track circuit for each direction of approach to said highway along each parallel track, capable when energized of detecting the presence of a trAin within approach warning limits, b. a warning signal means along said highway operable when actuated for displaying a signal warning highway users of the approach of a train, c. distance monitor means for at times individually supplying energy to a particular track circuit and responsive to the detection of a train therein for determining the distance of the approaching train from said highway, d. a mutliplexing means operable for sequentially coupling said distance monitor means individually to each separate track circuit, and e. a process controller means coupled for receiving the approaching train distance information from said distance monitor means and responsive thereto for actuating said warning signal means to display the warning signal when the train is a preselected minimum time period from said crossing.
 2. a shunt connected across the rails at the end of the corresponding section distant from the crossing.
 2. A protection arrangement as defined in claim 1 in which, a. energy supplied by said distance monitor means is an alternating current of preselected frequency, and b. each track circuit includes,
 2. a capacitor connected in series in the rail connections of said coupling transformer to inhibit the shunting of any other superposed track circuit of different frequency.
 3. A protection arrangement as defined in claim 2 in which, a. the separate track circuits for each direction of approach along each parallel track are paired as a center fed track circuit, coupled to the rails by a single transformer to form also a positive detector section including the actual crossing, b. each shunt at the distant end of each approach section is tuned to said preselected frequency, and c. the rail connections of each coupling transformer include a series capacitor selected to inhibit the shunting of any other superposed track circuit of different frequency.
 4. A protection arrangement as defined in claim 2 in which said multiplexing means includes, a. a bank of multiplexer relays controlled by said process controller means for operating through a predetermined sequence of conditions in repeated cycles, and b. a contact matrix controlled by said relay bank for completing a different circuit path through said matrix for each sequential condition of said relays, c. each said circuit path connected for supplying energy from said distance monitor means to a different track circuit to detect an approaching train in the corresponding section.
 5. A protection arrangement as defined in claim 4 which further includes, a. interface apparatus coupling said process controller means to said relay bank and to said warning signal means, and b. analog to digital converter means connected for receiving train distance signals from said distance monitor means and operable in response thereto for converting each signal from analog to digital form,
 6. A highway crossing protection arrangement for a plurality of highways intersecting in relatively close proximity a railroad track, comprising in combination, a. a warning signal means along each highway operable when actuated for displaying a signal warning highway users of the approach of a train, b. a normally deenergized detector track circuit for each crossing capable when energized of detecting a train approaching that crossing in either direction within limits of that track circuit, c. a shunt connected across the rails at a location along said track a selected distance in each direction away from all said plurality of crossings for defining the distant limits of each track circuit, d. distance monitor means for at times supplying energy to each track circuit and responsive to the detection of a train therein for determining the distance of that train from the associated highway crossing, e. a process cOntroller means coupled for receiving train distance information from said distance monitor means and responsive thereto for actuating a selected warning signal means to display the warning signal when an approaching train is a predetermined time interval from the corresponding crossing, and f. a multiplexing means operable for sequentially coupling said distance monitor means to each detector track circuit.
 7. A protection arrangement as defined in claim 6 in which, a. energy supplied by said distance monitor means is an alternating current of preselected frequency, b. each shunt at the distant ends of said track circuits is tuned to said preselected frequency, and c. each track circuit further includes,
 8. A protection arrangement as defined in claim 7 in which said multiplexing means comprises, a. a bank of multiplexer relays controlled by said process controller means for operating through a predetermined sequence of conditions in repeated cycles, and b. a contact matrix controlled by said relay bank for completing a different circuit path through said matrix for each sequential condition of said relays, c. each said circuit path connected for supplying energy from said distance monitor means to a different track circuit to detect a train.
 9. A protection arrangement as defined in claim 8 in which, a. said process controller means is a digital data process controller, and which further includes, b. interface apparatus coupling the process controller output to said multiplex relay bank and to said warning device, and c. analog to digital converter means coupling said distance monitor means through said interface apparatus to said process controller and operable for changing the distance signal output of said distance monitor means from analog to digital form. 